In recent years, light regulating glass capable of controlling penetration of sunlight rays has become a topic of interest for energy conservation, comfort, etc. The present specification will refer mainly to window glass to be used for windows in buildings, automobiles and the like, but the laminated bodies of the invention are widely applicable, with no limitation to windows.
The present inventors focused on the fact that windows are directly exposed to sunlight rays. By effectively utilizing the temperature difference between the presence and absence of solar radiation and between seasons, it became possible to develop revolutionary self-responding light regulating laminated bodies which, when exposed to sunlight rays in the high temperature summer season, naturally become opaque and block the sunlight rays. More specifically, for example, U.S. Pat. No. 5,615,040 (corresponding to Japanese Unexamined Patent Publication HEI No. 6-255016) is cited in Journal of Japan Solar Energy Society, Taiyo Energy, Vol. 27, No. 5 (2001), pp. 14–20. The basic structure of the invention described therein is a laminated body in which an isotropic aqueous solution is sealed between a pair of plates. The isotropic aqueous solution comprises at least a water-soluble polysaccharide derivative, an amphipathic substance and water. The principle depends on a stably reversible temperature-dependent sol-gel phase transition. At low temperature, the molecules are uniformly dissolved to produce an isotropic aqueous solution (sol state), while at high temperature a phase transition occurs as the dissolved molecules aggregate into a flocculated state (gel state). In the gel state, the difference in density between the solvent and the fine aggregates creates opacity due to light scattering, thereby blocking about 80% of light. When the laminated body is used to construct a window, the transparent state is maintained to permit penetration of sunshine when the temperature of the laminated body remains lower in the winter season, while heating by direct sunlight rays during the summer season produces opacity which cuts approximately 80% of the sun's rays, thereby providing an energy-conserving, light-regulating window glass. The laminated body satisfies the following fundamental conditions also listed in the aforementioned document.
1) Phase changes between the transparent and opaque state must be reversible.
2) Reversible changes must be able to be repeated without phase separation.
3) The material must be weather resistant.
This laminated body has already been tested as window glass by the present inventors, but it was found that the weather resistance needed to be further improved for it to be suitable for common use as window glass which is exposed to constant sunlight. The results of actual rooftop exposure testing in a Tokyo district using a laminated body assembled with a satisfactory sealed structure indicated an increase in the initial opacity temperature already within about 3 years, even with 5 mm-thick float glass. The present inventors diligently examined methods of adding ultraviolet absorbers to the isotropic aqueous solution and as a result succeeded in developing a laminated body exhibiting revolutionary high weather resistance having features 1) and 2) above, and adequately satisfying condition 3) above.
Window glass must exhibit high weather resistance for use over long periods of 10 years or more and even 20 or 30 years. It should also be as light and thin as possible for reduced load on building frames and compatibility with window frames, as well as for more advantageous manufacturing, transport, construction and the like. The present inventors had also previously examined methods of imparting glass panels with ultraviolet-blocking functions, but because of problems of such as coloring and weight increase and the need for special working, such methods were not generally suitable. The present inventors therefore conducted more detailed examination focusing on various ultraviolet absorbers in order to vastly improve the weather resistance of the isotropic aqueous solution itself.
Previously, there have existed only written references to the general concept of adding ultraviolet absorbers that dissolve in isotropic aqueous solutions for improved weather resistance (benzophenone derivatives, benzotriazole derivatives, salicylic acid ester derivatives, etc.), as also referred to by the present inventors in the aforementioned document, and the patent document mentions only Sumisorb·110S (2-hydroxy-4-methoxybenzophenone-5-sulfonic acid) by Sumitomo Chemical Co., Ltd. as a water-soluble ultraviolet absorber. We therefore tested two types of laminated bodies, comprising an isotropic aqueous solution containing no ultraviolet absorber or an isotropic aqueous solution containing Sumisorb·110S by Sumitomo Chemical Co., Ltd., by an ultraviolet exposure test as described in the examples, and found that air bubbles were generated in both cases from about 50 hours to 100 hours, producing unrecoverable irregularities.